The compound 5-[(R)-2-(5,6-diethyl-indan-2-ylamino)-1-hydroxyethyl]-8-hydroxy-(1H)-quinolin-2-one, which is known as Indacaterol (INN), and its corresponding salts are beta-selective adrenoceptor agonists with a potent bronchodilating activity. Indacaterol is especially useful for the treatment of asthma and chronic obstructive pulmonary disease (COPD) and is sold commercially as the maleate salt.
WO 00/75114 and WO 2004/076422 describe the preparation of Indacaterol for the first time through the process:

The condensation between the indanolamine and the quinolone epoxide leads to the desired product but always with the presence of a significant amount of impurities, the most significant being the dimer impurity, which is the consequence of a second addition of the product initially obtained with another quinolone epoxide, as well as the formation of another isomer which is the result of the addition of the indanolamine to the secondary carbon of the epoxide.
In addition, the reaction conditions to achieve the opening of the epoxide require high energies (ex. 21 of WO 00/75114) with temperatures of 110° C. or more for several hours, which favours the appearance of impurities.
WO 2004/076422 discloses the purification of the reaction mixture by the initial formation of a salt with an acid, such as tartaric acid or benzoic acid, hydrogenation and final formation of the maleate salt. However, the yield achieved by the end of the process is only 49% overall.
It has been found that impurities of tartrate and benzoate salts can exist in the final product as a result of displacing the tartrate or benzoate with maleate without prior neutralization to Indacaterol base. In addition, WO 2004/076422 discloses that proceeding via the free base of Indacaterol is not viable due to its instability in organic solvents. WO 00/75114 does disclose a method proceeding via the Indacaterol free base, but it is not isolated in solid form.
WO 2004/076422 furthermore discloses the method for obtaining the quinolone epoxide from the corresponding α-haloacetyl compound by reduction in the presence of a chiral catalyst, such as an oxazaborolidine compound, by proceeding via the α-halohydroxy compound.
There exists, therefore, the need to develop an improved process for obtaining Indacaterol and salts thereof, which overcomes some or all of the problems associated with known methods from the state of the art. More particularly, there exists the need for a process for obtaining Indacaterol and pharmaceutically acceptable salts thereof, which results in a higher yield and/or having fewer impurities in the form of the dimer and regioisomers impurities and/or salts other than the desired pharmaceutically acceptable salt.